Magic lantern slides are fragile objects consisting of transparent images depicted on thin glass plates to be projected by magic lanterns. Despite their widespread presence in archives and museums, these collections are often undervalued and understudied. The Portuguese Cinematheque holds the most extensive collection of slides in Portugal. This article presents the first preventive conservation case study focused on the collection of painted slides, reflecting on the general origins of this collection, examining the challenges faced by caretakers when adapting historical buildings to accommodate collections of this nature. Environmental monitoring of light and radiation, temperature, and relative humidity in storage and exhibition rooms was combined with ultraviolet-visible spectroscopy to measure the fading of one of the most light-sensitive colours identified in these slides in previous studies, the pink eosin-based lake, by comparing a slide exhibited under the measured light conditions with one kept in storage during the same period. The results identified damaging light exposure in display areas with illuminance values far above the recommended levels for these materials, and significant RH fluctuations in both spaces. These conditions are consistent with deterioration factors known to affect the material that composes these fragile media (e.g., light-sensitive painting materials and organic frames, and unstable glass). This study also showcases how raising awareness on the fragility of this heritage stimulated discussions and encouraged small and feasible changes that can positively impact its preservation.
Santos et al. (Tue,) studied this question.
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